Process for producing superior cast iron



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BY h United States Patent PROCESS FOR PRODUCING SUPERIOR CAST IRON William H. Moore, Larchmont, N. Y., assignor to Meehanite Metal Corporation, a corporation of Tennessee Application April 22, 1954,, Serial No. 424,809

7 Claims. (Cl. 75-130) This invention relates to the manufacture of high duty gray iron castings of controlled physical properties, not subject to the structural weakness resulting from mass influence, common to a commercial gray cast iron.

Generally, cast iron is produced from scrap and pig iron mixes melted in a cupola furnace or even directly from molten pig irons melted in a blast furnace. Such a cast iron is a comparatively weak brittle material, having little to recommend it as an engineering material and varying considerably in its structural makeup from casting to casting, or even within any single casting. This variation in structure is largely due to the amount and form of the graphite flake, which is found in a normal gray cast iron, and to the difficulties of controlling this element.

The introduction of steel into the cupola charge and improved control of the analysis of cast iron with respect to the chemical elements that control graphitization, represents a step in the direction of an improved engineering product. Briefly, the introduction of steel into hitherto high pig iron charges has led to a lowering of the total carbon content and, therefore, a lowering of both the amount and the size of the weakening graphite flakes.

Unfortunately, the indiscriminate use of steel in the charge often results in excess hardness, weakness, excessive shrinkage and gasification in the cast iron. This has led to the process of graphitization or inoculation by graphitizing materials, prior to the pouring of the cast iron. It has been found that the judicious use of late inoculants leads to superior mechanical properties in the cast iron. This step may be regarded as a most significant one in the art of producing engineering types of cast iron, although these cast irons, while produced by a process of inoculation are still subject to high physical property variation, undesirable graphite structure, gasification defects, poor fluidity, and excessive contamination with non-metallic impurities.

Over a period of years, many eminent metallurgists devoted their attention to the mechanism and the control of the structural constituents of cast iron, during the process of solidification, from the molten to the solid condition.

There are three major variables involved in this:

1. The nature of the charge melted. 2. The chemical composition. 3. The rate of cooling of the, casting in the mold.

Various formulas have been developed for relatingthe chemical composition of the iron to the cooling rate or the section of the casting. Unfortunately, only the simplest of shapes is found to have a defined cooling rate, and it was soon found that chemical composition could not be adjusted sufliciently to ensure a uniform and dependable microstructure in all castings. Some improvement resulted from the combined control of chemical composition and late inoculation, but it was found that castings of varying sect-ions which exhibit varying cooling 2 rates, could not be controlled with any degree of exactitude.

The question of the nature of the charge materials has been given considerable attention and many th'eories have been put forward to explain the mechanism of solidifi'ca tion of cast iron. Thus, it has been postulated that graphitization is largely dependent on the presence of nuclei in the melt. These nuclei have been described as being silicates, undissolved carbon particles, and even gases contained in the iron. It has been shown that superheating, Washing with inert gases, and removal of silicates, could materially affect the mode of graphitization of the cast iron. It has been generally accepted by metallurgists skilled in the art, that complete and positive control of gray cast iron structures is only possible where the degree of nucleation of the cast iron is a constant or a known factor. This degree of nucleation originates with the nature of the charge materials, condition of melting and other factors.

The most significant recent improvement in gray iron structure control is undoubtedly the process outlined by Smalley et al. in U. S. Patent No. 2,371,654. In this patent, the basic concept of constitution is outlined and a dual control of both constitutional and process carbide values in relation to the casting section and the physical properties desired is taught. This positive control method is entirely new in the field of cast iron metallurgy and has resulted in a startling improvement in the structural uniforrnity of cast irons.

This Smalley et al. discovery, was basic in its origin and disclosed the conception of constitutional and graphitized carbide values related to the casting section, and this invention constitutes an advance in the art and sets forth a new method of how to obtain these ratios in practice. The carbide values discussed herein may be obtained by the wedge procedure disclosed in Smalley et al., U. S. Patent No. 2,371,654 or by any other method known in the art.

It is an object of this invention to provide a positive predetermined control of constitutional carbide value, a positive control of the graphitized carbide value, and a positive control of the structural components of a cast iron, as influenced by mass action. It is a further object to described a method of obtaining cast iron of constant predetermined and reproduceable physical properties. Other objects of this invention will be apparent on the reading of the specification and drawing in which:

Figure 1 is one of many ways of illustrating the principles involved and is a graph having as ordinates carbide value as measured on a 28 /2 test wedge, and graphite solution index. The 'graphitic solution index is the percentage of graphitic carbon in the charge plus one-tenth the carbon equivalent of the charge. The carbon equivalent here is total carbon plus one-third silicon; and

Figure 2 is illustrative of a method of relating chemical element changes with carbide value and is a graph having as ordinates carbide value as measured on a 28 /2 test wedge, and chemical change ratio. The chemical change ratio is an empirical relationship and equals three times the silicon loss percentage on melting, plus twice the manganese loss percentage in melting, minus the carbon gain percentage on melting.

All charges used in establishing this particular graph had a 1.70 graphite solution index.

Briefly, my invention comprises:

(a) Establishing a means of graphite control of the charge to insure a predictable carbide value on melting.

(b) The controlled addition and solution'of the graphitizer on a positive basis to a graphitized or processed carbide value, related to the constitutional carbide value, to the section of the casting, and the physical properties desired. 1 .1

3 Calculation of charge composition As those skilled in the art will readily appreciate, the carbide value obtained on a test wedge which has fixed dimensions and a constant cooling rate, is dependent on the physical constitution of the metal as well as on the chemical composition. Thus, with a fixed chemical composition, the carbide value will vary as the physical constitution of the cast iron varies, Whereas with a fixed physical constitution the carbide value will vary as the chemical composition varies.

The carbide value, determined by a fractured wedge test, is a function of the degree of surfusion or undercooling with respect to graphite solution in passing from the liquid to the solid state. Thus, a high graphite value represents a strong degree of undercooling, whereas a low carbide value represents a return to normal condition of solidification. This degree of surfusion or undercooling, during the process of solidification, is influenced by the nature of the materials charged, its chemical composition, and the conditions obtaining during the melting of the charge.

As the precipitation of graphite from molten metal, to give a gray iron, is in part dependent on the presence and action of nucleating substances in the melt, it follows that the presence or absence of such nucleating substances will exert a profound effect on the physical constitution of the metal and on the constitutional carbide wedge. Thus, a metal high in nucleating material concentration will give a low carbide wedge, whereas a metal low in nucleating material concentration will give a high carbide wedge. In short, the physical constitution of a cast iron, that is its degree of undercooling, is in the main determined by the concentration of nucleating material that is present in the molten metal at the time of change of state from the liquid to solid condition.

This conception is quite straightforward because the deliberate introduction of nucleating material as in the process of inoculation, immediately lowers the chill value of the metal. Likewise, the presence or otherwise of nucleating material in the original melt will directly influence its inherent carbide value.

The calculation and control of chemical composition of the cupola charges in the process of my invention is based on the initial control of the nucleating substances present. The major emphasis on control is based on the graphitic carbon content of the charge.

It is well known that graphite is an extremely refractory material and also that its complete solution into a molten ferrous bath requires time. In addition to this, its solution rate is a direct function of both temperature and composition.

In a cupola furnace, melting is extremely rapid, and the molten metal is removed from the furnace soon after melting. This time of removal will vary according to the size of the furnace and holding capacity of the Well, but is in any case, by all standards, a relatively short time.

Graphite flakes in the original charge material thus can, because of incomplete solution, pass through into the final molten metal without being completely dissolved. They can then act as nucleating material in the final solidification of the cast iron resulting then in an effective manner to lower the physical constitution or the carbide value of the molten metal.

As previously mentioned, the solution of graphite during melting is controlled by the time, the temperature, and the carbon saturation value of the charge. Thus, the solution of the graphite is lower as the graphite content of the charge is higher, and is higher as the graphite content of the charge is lower, everything else being equal.

While the nucleating effect of other substances, such as suspended silicates, cannot be ignored, I have found for all practical purposes, the effect of graphite nuclei is so potent, that control of the solution of these nuclei during melting at once results in a positive control of the constitutional carbide value of the molten composition.

Thus, the first step in my improved process lies in the control of the graphitic carbon content of the charge so as to effectively control the solution of the graphite nuclei during melting, and provide a molten metal of controlled carbide value.

As the rate of solution of the graphite during melting is also dependent on the composition of the charge, 1 find it desirable to allow for the carbon content of the charge in terms of the well-known carbon equivalent factor, i. e., carbon plus one-third of the silicon content for ordinary materials.

Thus, the first step is to calculate the graphitic carbon content of the charge and then modify its value according to the carbon equivalent content of the charge to provide a graphite solution index which is used as a focal point in controi. The exact calculation may, of course, be made in a number of ways, but the important feature of my invention is to relate the graphitic carbon content of the charge and the carbon equivalent content of the charge in such a way as to provide an index of graphite solution during melting. By way of example:

Thus, the percentage of graphitic carbon in this charge is 1.085 and this has to be modified to obtain the graphite solution index. With a silicon content of 1.50 in the charge, the total charged carbon equivalent is 1.71 plus /s 1.5O), or 2.21%. Forpractical purposes, I have found that adding of this equivalent to the percentage of graphitic carbon, gives a reliable graphite solution index. Thus, for this charge the graphite solution. index is 1.085 plus (2.21 divided by 10), or 1.306%.

I do not wish to limit myself to any exact method of calculation because as those skilled in the art will appreciate, many different correction factors would be up erative, providing the graphite of the charge was always related to the obtained carbide value.

In a series of very carefully controlled melts where the graphite solution index was calculated and the re sultant carbide value was measured, on wedge pieces having a 28 /2 acute angle, the results shown in Figure 1 were obtained. I have since used this relationship as a basis of constitutional carbide control in commercial practice and have always found it to give consistent re sults. The particular relationship in Figure 1 is confined to cast iron coming within the range of normal composition variation.

The first step of my invention is the adjustment of the charge composition with regards to the graphitic carbon content as indicated. This establishes an initial control on the available nuclei content of the charge, and provides a dependable means of controlling the degree of undercooling or the true physical constitution of the molten metal. The constitutional carbide value is measured by means of the wedge tests commonly used by those skilled in the art.

Melting of the charge The constitutional carbide value of the molten cast iron can be modified by the process of melting. This is because the melting process itself may alter the number of nuclei available in the melt and so modify the degree of surfusion or undercooling.

It is common practice for those skilled in the art to set up the melting process so as to give reasonable arcane constant changes in the chemicalcomposition of the cast iron during the process of melting. Thus, under Well regulated melting conditions, it will be found that the elements carbon, silicon, manganese, and even sulphur and phosphorus, vary. within restricted limits.

The elements silicon, manganese and carbon are of particular importance, and it is usual to lose silicon and manganese during melting while carbon may be increased. The degree to which these elements. vary has a direct effect on the carbide value obtained when melting a given charge.

By adjusting the melting in the manner of those skilled in the art, it is possible to vary the degree of change obtained in the chemical elements and consequently, the carbide value of the molten metal. It is common prac tice to reduce all melting variances to a constant value so as to eliminate as nearly as possible the variances in chemical elements during the melting.

In the process of my invention, it is possible to modify the constitutional carbide value by the process of melting, but for each condition of melting the constitutional carbide value will be found to vary directly with the graphite solution index of the charge. Thus, a variation in the condition of melting merely means that a new relationship must be established to correlate the graphitic carbon content of the charge with the constitutional carbide value. It does not affect in any way the basic invention of controlling the graphitic carbon of, the charge to control the degree of surfusion or undercooling.

As a further aid to controlling the constitutional carbide value by control of the graphite content of the charge, I have found that the exact effect of the melting condition on. the constitutional carbide value can readily be allowed for.

Figure 2 indicates that the carbide value may be altered by a variation in the change in chemical elements during the melting process. In Figure 2, the change in chemical elements has been calculated as a simple formula, namely, three times the silicon loss per cent plus two times the manganese loss per cent, minus the carbon gain per cent. I have found that this formula provides a convenient measure of the degree of change in. the chemical elements during melting. The results shown in Figure 2 were obtained from a series of melts where the graphitic carbon content of the charge, as expressed by the graphite solution index, was kept constant, but where the melting was varied so as to change the element losses and gains. The carbide value was measured by means of a wedge test.

On the basis of the relationship shown in Figure 2, I have found that an increase of in the chemical change :ratio will result in an increase of 2-2 /2/32nds in the carbide value of the metal. A decrease of 10 in the chemical change ratio will result in .a decrease of 22% /32nds in the carbide value of the metal.

If, therefore, a change in the chemical elements on melting is unavoidable because of a change in the coke quality, acidity of basicity of the slag, speed of melt, and other factors, it is possible to determine the degree of this change and adjust the charge with respect to the graphitic carbon content so as to provide a controlled constitutional carbide value in the melted metal.

An example of this type of adjustment as applied under the teachings of my invention, is given herewith:

A seiies of charges were placed in the cupola "to give To do this, the charge value was adjusted according to Figure. 2 to.

a constitutional carbide value of have a graphite solution index of 1.50. Melting control in the cupola normally resulted in a chemical change ratio of 30 which gave the desired constitutional carbide,

value of approximately ofthe heat, it was found that the melting change ratio increased to 50 and the constitutional carbide value was higher than that desired. i

As the quality of coke used for melting made it difficult to maintain the normal chemical loss ratio, 30, it was necessary to alter the charge at the end of the heat to give a lower constitutional carbide value so as to offset the gain in constitutional carbide value produced by the melting at this stage of the heat.

Reference to Figure 2 shows this gain to be approximately for the change of from 30 to 50 in the melting loss ratio. For a desired constitutional carbide value of therefore, the solution index of the charge would have to be changed to give a 35 constitutional carbide value. The charge at the end of the heat was then al tered to give a graphite solution index of 2.0. This with the chemical change ratio of 50, resulted in a constitutional carbide value of approximately as desired.

Thus, in the practice of my invention, the graphite content of the charge may be varied to give a defined constitutional carbide value under any defined condition of melting. i

Controlled nucleation or graphitization of the melt Nucleation of molten cast iron with a graphitizing additive is perhaps the most common procedure in the manufacture of high test cast iron. It is a subject that has received much attention from both research and practical metallurgists during the past two decades.

Nucleation relates to the addition of substances which act directly to nucleate the graphite either through direct chemical combination with the molten iron or which function through a gaseous reaction causing the formation of unstable carbides, or it may influence certain thermal factors during freezing of the eutectic. It has been contended by some that it may even create nuclei of a certain crystal structure for the graphite to deposit on.

In the absence of nucleation, the molten iron has a strong tendency to vary considerably with respect to the deposition of graphite. As has been pointed out, I have discovered that by controlling the quantity of graphite nuclei introduced in the cupola charge, I am able to control the degree of surfusion during solidification thereby obtaining an iron of controlled constitutional carbide value. With such a base material, I thus have a positive control of the carbide elfect wedge thereby establishing a sound yardstick for the final step of controlling the nucleation of the graphite in the finished casting to an exact degree. This second stage of controlling the nucleation of the graphite by means of an additive is,

however, old in the art, but nucleation so as to provide controlled final graphitization on a positive basis to a predetermined value still presents many unsolved probems.

In all existing processes, the additive is introduced in the molten iron as it runs down the furnace spout or directly into the ladle. Whether its action is one of depending upon chemical solution, reaction with volatile gases, or the creation of nuclei of a certain given structure, it is rarely that 50% of that added is eflective, while it is not uncommon for over to be lost through oxidation, slag contamination or by flotation. It is quite common in practice to add several times the quantity of additive that is known to be necessary because of these recovery and effect uncertainties. In my discovery, the whole of the additive is effective, being quickly taken into complete solution, hence accomplishes the desired end and that is a degree of controlled graphitization to a predetermined value. This means an exact amount can be estimated and added with positive end results and such a small amount is required that undue changes in chemical composition of the finished castings are avoided while considerable economies are effected in cost of the manufacture.

In addition to this, any changes in chemical composi .'7 tion of the iron itself that does occur may be allowed for by consideration of the chemical change ratio and reference to the type of relationship as shown in Figure 2.

In the manufacture of a casting having very heavy and very light sections, the constitutional carbide value was adjusted by control of the graphite content of the charge so as to ensure solidity in the heavy section of the casting. On the other hand, the process carbide value had to be adjusted to a low value to ensure machinability in the lightest section of the casting. This called for a heavier than normal addition of a nucleating substance. Such an addition of a nucleating substance would result in a change in the silicon content of the metal which would amount to an increase of 0.15%. The original metal was melted to a chemical change ratio of 30 which involved a silicon loss of 15%, a manganese loss of 25%, and a carbon pick up of 65%. The increased silicon addition by graphitization reduced the overall silicon loss to a value of 10%, resulting then in a chemical change ratio of 3 10% plus 2 2S% minus 65% or 15. On Figure 2, this corresponds to a change in carbide value of produced by the change in composition during nucleation. Any further change in carbide value during treatment was directly due to nucleation rather than to change in composition.

Any normal silicon base graphitizing material is operative in the process of my invention, but I prefer to use the silicides of the alkaline earths. Examples of Such silicides are calcium silicide, magnesium silicide, zirconium silicide, and titanium silicide.

For example, in a series of tests I added 80 ounces per ton of varying mixtures to a molten metal produced from a charge having a graphite solution index of 1.0 and a constitutional carbide value of The additions made graphitized the metal to give the graphitized carbide values indicated in the following table:

Graphitized Wedge Value Additive Used Calcium silicide 3 parts Calcium fluoride 1 part" Calcium silicide 3 parts Sodium aluminum fluoride 1 part Zirconium silicon 2 parts Calcium fluoride 1 part Magnesium silicide 4 parts Sodium fluoride 1 part Iron silicide 3 parts Calcium fluoride 1 par Calcium silicide 3 part Iron silicide 4 parts Magnesium fluoride 1 part. Barium silicide 3 parts Calcium fluoride 1 part- Titanium silicon 3 parts. Calcium fluoride 1 part Nickel silicon 1 part. Magnesium fluoride 1 pa In addition to this, I have found that other silicides such as lithium and strontium silicide and silicon base materials, when used in conjunction with alkaline earth fluorides, are effective graphitizers, under the process of my invention.

As the process of my invention requires initial control to a defined constitutional carbide value, and then treatment with an addition to promote graphitization, it follows that this must be added in a manner that will ensure absolute and complete incorporation in the molten metal. This is of vital importance because the basis of obtaining good mechanical properties in castings of different sectional thicknesses is the positive relation of constitutional and graphitized carbide value to the section of the casting I and the level of physical properties desired. In the process of my invention I recognize this and use the basic teachings of Smalley et al. in U. S. Patent No. 2,371,654, but I provide a new novel means of obtaining these values with positive control.

It has been pointed out that graphite of carbon nuclei are extremely potent in promoting graphitiz-ation of a cast iron melt. This is recognized by those skilled in the art and in the process of my invention I prefer to use refractory carbides generated within the molten metal as nuclei for graphitization. I refer particularly to the carbides of the alkaline earth metals. As an example of this, calcium carbide is known as a refractory carbide which by virtue of its refractory nature, can exist in molten iron at high temperatures, and can, therefore, act as nuclei in the precipitation of graphite by controlling the degree of undercooling during solidification.

The addition of alkaline earth silicide, such as calcium silicide, to a molten cast iron results in the production of minute quantities of alkaline earth carbides, such as calcium carbide, in the molten metal. This has been recognized for some time, particularly because of the emission of carbide gas when fracturing test pieces made from a metal so treated.

It has been deduced, on theoretical grounds, that calcium silicate for example 'acts with carbon dissolved in the molten metal thus: CaSi2 plus 20 equals CaCz plus 2Si. This calcium carbide, being extremely refractory and minute, being formed so to speak in a nascent condition, becomes available to act as carbon nuclei for the subsequent precipitation of graphite. The exact mechanism is not completely understood, but it is probable that the metastability of this carbide causes a breakdown to carbon which initiates immediate graphitization by a process of seeding.

Whatever the actual mechanism of the action, it is, of course, readily apparent that the amount of carbide formed be under positive control so that the degree of nucleation is under positive control. To ensure this, the alkaline earth silicide, such as calcium silicide, must be introduced into the melt in such a manner that its solution is complete and the formation of alkaline earth carbides, such as calcium carbide, in a fine state of subdivision, is at a maximum and constant value.

The complete and effective solution of alkaline earth silicides and other alkaline earth materials, has long been a matter of concern to the practical metallurgist. Various methods have been suggested for complete mechanical incorporation of these silicides, but it has been found that such methods are not fully effective.

In my co-pending application, U. S. Serial No. 347,994, now abandoned, entitled Carrier Process for Metallurgical Alloy Additions, it has been disclosed that certain fluorides of alkaline earths and rare earths, as well as other compounds of these elements, may be used for the introduction of alkaline earth silicides and carbides into the molten metal. This carrier process is particularly concerned with the introduction of large amounts of alkaline earth materials into the metal, so as to completely change the nature and the form of the graphite flake.

In the process of this present invention, I am concerned only with the introduction of small amounts of alkaline earth silicides such as calcium silicide, or silicon base graphitizers such as ferro silicon, magnesium silicon and zirconium silicon, for the purposes of nucleation and graphitization. I prefer particularly for economical reasons, to use a mixture of calcium silicide and a mineral fluoride such as magnesium, sodium, aluminum, calcium, or potassium fluorides, as an additive material for nucleation.

In a carefully controlled test, the working of such a nucleating mixture was demonstrated. In test A, a portion of a bath was poured on to a quantity of calcium silicide of 5% of the weight of the bath portion. The resultant slag on the metal surface was collected for examination. In test B, a second portion of this same bath was poured on a 5% by weight of a mixture of calcium silicide and powder fluoride. This mixture contained 2 parts of calcium silicide to 1 part of fluoride. The resultant slag on the metal surface was collected for examination. In addition to this, in test C a sample of the calcium silicide itself was retained for examination.

On examination and chemical analysis of these slags and of the calcium silicide itself, it was found that:

Test A.-Calcium silicide contained .12% carbon, but did not contain any calcium carbide.

Test B.--Calcium silicide slag contained 1.71% carbon and approximately 1% of calcium carbide.

Test C.-Calcium silicide slag containing fluoride contained 3.20% carbon and approximately 1 /2 to 2% calcium carbide.

These tests illustrate that the selective use of fluorides aids in the production of calcium carbide when calcium silicide is added to the metal. As I desire to produce these carbides in the process of my invention, I prefer to use a mixture of alkaline earth silicides, such as calcium silicide and alkaline earth fluoride, such as cryolite, magnesium, calcium fluoride, for my graphitizing addition, which is the final step of the process of my invention.

The use of a mixture of an alkaline earth silicide, such as calcium silicide, and an alkaline earth fluoride such as calcium fluoride, has resulted in several other advantages not normally obtained in the process of graphitizing by nucleation.

In the first place, the alloy recovery from such an addition is more than 95% eflicient. This allows accurate estimation and control of the chemical compositional effect so that it may be differentiated from the constitutional to graphitized carbide effect produced by nucleation.

In the second place, the mixture results in complete solution of the addition without build up of excess nucleating material in the furnace spout or in the ladle, depending on where the addition is made. Avoiding of build up at the addition point ensures complete and controlled graphitization at all times. Where a purely mechanical addition is conducted, such build up, particularly in a furnace runway, disturbs the degree of contact between the additive .and the metal, thus giving variable and uncontrolled results. In my preferred method, as described, such inconsistencies are obviated.

In the third place, the action of the alkaline earth silicide-fluoride mixture is exothermic in nature. This allows the addition of any amount of nucleating material without any decrease in the temperature of the metal. On the contrary, I have found that an addition of /2 to 1% of such a mixture has increased the fluidity of the molten metal as much as 25-50%. Alkaline earth sili cides used by themselves, without alkaline earth fluorides,

require high temperatures in the molten metal for better absorption. The degree of absorption will thus vary from heat to heat or even during any one heat, according to the temperature of the molten metal. With my preferred method, involving a combination of alkaline earth silicide and fluoride, the incorporation is not dependent on the temperature of the metal, as the reaction is exothermic and supplies its own heat for solution. I am thus able to avoid a major cause of variation in the nucleating and graphitizing process.

In the fourth place, the action of the alkaline earth rich slag produced by my addition, is a cleansing and scouring one. Such a slag avidly absorbs oxides, silicates, sulphides, and the like, and provides a practical means of cleansing the molten metal. In actual practice, the preferred addition of my invention has resulted in reduction and elimination of surface slag defects previously found on castings produced by more conventional nucleation procedures.

In the fifth place, complete degasification of the molten iron is obtained, which results in a fluid self-feeding iron greately superior to an iron not so treated.

The amount of the nucleating addition, in the process of my invention, is adjusted according to the degree of nucleation required in reducing the constitutional carbide value to the processed or graphitized carbide value.

I have been able to determine the degree of nucleating required in a practical manner by the statistical study of graphitizing additions where the charges have been adjusted for graphite content and the melting process hasbeen under control.

I normally add between 100 ounces per ton (based on alkaline earth silicide content) for carbide chill value reductions in the ratio of 4:1, 70 ounces per ton for re ductions in the ratio of 3:1, and 40 ounces per ton for reductions in a ratio of less than 3:1.

However, the preferred method of addition of alkaline earth silicide as practiced in my invention, always ensures absolutely reproduceable results as measured in terms of the degree of reduction in carbide value from the constitu-- tional carbide value to the processed or graphitized carbide value.

Although this invention has been described in its prc-- ferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by. way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

l. The process of making cast iron to a predetermined carbide value, comprising the steps of, selecting a carbide value greater than said predetermined carbide value and falling in the range of related values bearing a ratio to those values between the lines shown in Figure l, charging a furnace with materials having a graphite solution index between zero and 4.0 to give said greater carbide value according to related values bearing a ratio to those values between the lines shown in Figure l, and sub stantially maintaining said greater carbide value by also charging the furnace with materials to produce a chemical change ratio of related values bearing a ratio to those values between the lines as shown in Figure 2 at said greater carbide value, melting said charge, and then graphitizing the melt to substantially said. predetermined value with an alkaline-earth silicide in combination with an alkaline-earth fluoride.

2. The process of making cast iron to a predetermined carbide value, comprising the steps of, selecting a carbide value greater than said predetermined carbide value and falling in the range of related values bearing a ratio to those values between the lines shown in Figure 2, charging a furnace with materials having a chemical change ratio of related values bearing a ratio to those values between the lines as shown in Figure 2 between zero and to give said greater carbide value according to related values bearing a ratio to those values between the lines shown in Figure 2, and substantially maintaining said greater carbide value by also charging the furnace with materials to produce a graphite solution index of related values bearing a ratio to those values between the lines as shown in Figure l at said greater carbide value, melting said charge, and then graphitizing the melt to substantially said predetermined value with an alkalineearth silicide in combination with an alkaline-earth fluoride.

3. A process of producing cast iron of a predetermined carbide value characterized by selecting a carbide value greater than said predetermined carbide value and falling in the range of related values bearing a ratio to those values between the lines shown in Figure 2, charging a furnace with materials having a graphite solution index falling within the range of related values bearing a ratio to those values between the lines in Figure l and simultaneously having a chemical change ratio falling within the range of related values bearing a ratio to those values between the lines shown in Figure 2, said graphite solu-- tion index and said chemical change ratio being related. to each other to give said greater carbide value accord-- ing to related values bearing a ratio to those values be tween the lines shown in Figures 1 and 2, respectively, and then graphitizing said cast iron to substantially said predetermined carbide value with an alkaline-earth silicide in combination with an alkaline-earth fluoride.

4. A process of producing cast iron of a predetermined carbide value characterized by selecting a carbide value greater than said predetermined carbide value and falling in the range of related values bearing a ratio to those values between the lines shown in Figure 2, charging a furnace with materials having a graphite solution index falling within the range of related values bearing a ratio to those values between the lines shown in Figure l and simultaneously having a chemical change ratio falling within the range of related values bearing a ratio to those values between the lines shown in Figure 2, said graphite solution index and said chemical change ratio being related to each other to give said greater carbide value according to related values bearing a ratio to those values between the lines shown in Figures 1 and 2, respectively, and then graphitizing said cast iron to substantially said predetermined carbide value with an alkaline-earth silicide in combination with an alkaline-earth fluoride by using approximately 100 to 70 ounces per ton of alkaline earth-silicide content for carbide value reductions falling between the ratio of four-to-one and three-to-one and approximately 70 to 40 ounces per ton for carbide value reductions falling in a ratio less than three-to-one.

5. The process of making cast iron to a predetermined carbide value, comprising the steps of, selecting a carbide value greater than said predetermined carbide value and falling in the range of related values bearing a ratio to those values between the lines shown in Figure 2, charging a furnace with materials having both a graphite solution index and a chemical change ratio, the graphite solution index and the chemical change ratio being of related values to produce substantially said greater carbide value according to related values bearing a ratio to those values between the lines shown in Figures 1 and 2, respectively, melting said charge, and then graphitizing the melt to substantially said predetermined value with 12 an alkaline-earth silicide in combination with an alkalineearth fluoride.

6. The process of producing cast iron of predetermined carbide value characterized by selecting a greater carbide value than said predetermined value, selecting a charge of graphitic carbon content and carbon equivalent to give said greater carbide value and falling in the range of related values bearing a ratio to those values between the lines as shown in Figure l and further characterized by selecting the charge to produce chemical changes of silicon, manganese and carbon to give said greater carbide value and falling in the range of related values bearing a ratio to those values between the lines as shown in Figure 2, melting said charge, and then graphitizing the melt with an alkaline-earth silicide in combination with an alkaline-earth fluoride to substantially said predetermined carbide value. I

7. The process of producing cast iron of predetermined carbide value characterized by selecting a greater carbide value than said predetermined value, selecting a charge of graphitic carbon content and carbon equivalent to give said greater carbide value and falling in the range of related values bearing a ratio to those values between the lines as shown in Figure 1 and further characterized by selecting the charge to produce chemical changes of silicon, manganese and carbon to give said greater carbide value and falling in the range of related values hearing a ratio to those values between the lines as shown in Figure 2, melting said charge, and then graphitizing the melt to substantially said predetermined carbide value.

References Cited in the file of this patent Foundry Practice, 3rd edition, pages 322 and 323. Edited by Palmer. Published in 1924 by John Wiley 3: Sons, Inc., New York. 

